Long Tail Pair Transistors

markzb · « **on:** 15 Apr 2004, 09:13 am »

Hi Everyone

I would be most grateful if someone could shed some light on how to go about selecting bipolar junction transistors for the input of a transistor amplifier....i.e. what characteristics are we looking for in the data sheets?

Also....does anyone have any favourites transistors for making up their long tail pairs?

What does everyone think of BC128L for starters?

Any tips would be most welcome.

Many thanks

Mark

Dan Banquer · « **Reply #1 on:** 15 Apr 2004, 02:23 pm »

My first question is how much voltage will be across the transistors?. The voltage from collector to emitter in this configuration will be a very important factor on what you need for transistors. Hope this helps.
d.b.

markzb · « **Reply #2 on:** 15 Apr 2004, 05:41 pm »

Hi Dan

Thanks very much for your reply. I am very much an amplifier newbie! For the moment, I am drawn to typically british amplifiers that are I suppose Class AB or B, that have supply rails of +/- 40V. Also, the long tail would be fed by a current source. I am trying to learn and further my understanding of why amps tend to be built the way they are and wanted to start at the long tail pair.

Cheers

mark

Dan Banquer · « **Reply #3 on:** 15 Apr 2004, 08:31 pm »

I could put up a really long post but I think it's best if you take the time and read a few texts that deal with this. I would recommend books by the late J.L. Linsley Hood on audio and linear electronics, also Doug Self's book on Power Amplifier Design, also if you can find it, The Class A design manual by William Snyder. These are just a few of the texts that cover this topic so enjoy the reading.
d.b.

markzb · « **Reply #4 on:** 16 Apr 2004, 12:39 am »

Hi Dan

Ive ordered the book by Douglas Self. Got another 5 weeks to go! Ive never heard of the class A design manual you speak of. I shall go and have a search and see

Would you have though any suggestions on what we be a good transistor to use here? What do you think of the BC182L I mentioned? Would that be a good choice in the application I spoke of, or is there something you feel might be even better to try out. Does it make much difference to the sound which transistors we choose to use here?

Thanks kindly

mark

Dan Banquer · « **Reply #5 on:** 16 Apr 2004, 02:04 pm »

If you read the data sheet for the BC 182 you will find that the maximum voltage from collector to emitter is 50 volts. If the circuit, and the power supply running the circuit will not exceed that parameter than yes you can use a BC182. What do you think might be some other important parameters?
d.b.

markzb · « **Reply #6 on:** 17 Apr 2004, 10:31 am »

Hi Dan

The parameter I was thinking about foremost after operational suitability was sound quality!

Do different transistors sound different in this application? Is there a particular transistor thats great to use here? Or theres hardly any difference between the various transistors sound wise?

Cheers

Mark

Dan Banquer · « **Reply #7 on:** 17 Apr 2004, 11:26 am »

Well I'm not really going to get into what someone else thinks about sound quality. But I am going to suggest that you start thinking about things like gain bandwidth, noise, biasing, etc.etc. This is work you need to do on your own for your education. You have a lot of reading and experimenting to do.
For all the years I have spent in electronics the learning never stops, which is what really makes a lot of this very enjoyable.
d.b.